I've been trying to identify a motor oil leak for months. I can see fresh oil where the transmission meets the engine. I've confirmed that it is not the rear main seal. I've replaced the gasket on the auxiliary port off the oil pan. The oil filter and drain bolt are not leaking. No leaking from the valve covers.

It would seem that the leak is coming from the oil pan gasket, though I can't see that area to be sure. The bolts on the oil pan (that I can see/reach) are tight.

Any other thoughts as to where the oil might be coming from? I've attached a few pictures to help.

It seems like replacing the oil pan is a big job. The front diff has to come out, as well as some big bolt on pieces to the frame, the tranny too? Driveline? Looks like a pretty big job.

Oil on engine starter bolt and surrounding area

Oil on engine starter bolt and surrounding area

Oil above oil filter

Oil above oil filter

Oil above oil filter

 

Just had rear main seal, and pan gasket replaced, $1,878, that was also with an ABS module 03 suburban 5.3.

 

why does the 1st and 2nd picture look so different? taken at different times maybe? could the intake be leaking down?

 

Yes the 1st and 2nd pix were taken at different times. I’ve been cleaning the oil up with brake cleaner every few days to aid in identifying the source. It’s not from the intake.

 

if its not coming from the lifter valley cover or valve covers it has to be from the rear main or oil pan. since you confirmed its not the rear main then that leaves the oil pan

 

remove the black plastic cover and then you can see the flex plate. if the flex plate is dry...the rear main seal is ok.

 

Thanks. Replacing the seal on the oil pan looks like a big job. Local transmission mechanic I was referred to said around $600. Sound about right?

 

Thanks. Replacing the seal on the oil pan looks like a big job. Local transmission mechanic I was referred to said around $600. Sound about right?

 

the labour time for a 4wd is 4hrs iirc. the front diff must be removed.

 

Update on this issue. I had the oil pan gasket replaced. That job was pretty straightforward. This model has 4 wheel drive and the mechanic and I noticed both front diff seals were leaking slightly. I had the passenger side diff seal replaced just a few months ago, so I was part confused and part pissed.

While the mechanic was getting the diff out of the way, he investigated the diff seal leaks. The passenger seal looked fine, but the diff oil was milky indicating water in the diff. He kept looking and saw that the vent tube on the diff had become disconnected and water had gotten into the diff. The vent itself was now blocked with road grime. And the vent tube was blocked with road grime.

Luckily it does not look like any internal damage to the diff. He cleaned everything and reattached the vent to the diff.
His theory is that because the diff wasn't venting, under certain conditions pressure was building in the diff and pushing fluid past the seals, hence the leak we were seeing. I'll keep on eye on that.
Total labor for all this was about $550. He has used a local parts supplier for the past 40 years, so instead of getting a $40 gasket from gm-parts direct online, the gasket cost me $130.